This one is the squishy mystery for Jehovah's Witnesses.
Most faithful JW's see the 'anointed' and in particular the Governing Body as angels in human form. They were chosen by God and are being 'used' by Holy Spirit.
We earthlings can't understand how God chooses and anoints (with Holy Spirit) these people. We can't understand how God uses his Holy Spirit to direct them what to write or what rules/policies to create.
It's a mystery. Just accept it.
"And now, brothers, please pass the contribution box around."
ginger